The battery in that nearly 10-year old iPad may have failed.
iPad is too old and not worth anything in sell/trade-in value.
Any costs for any type of battery replacement would NOT be a worthwhile endeavour.
This year and model iPad is simply too old and obsolete and no longer supported by Apple or any third party app developers.
Sorry.
It is past mid 2022, now.
You really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted Apple product/device retailers/resellers, some locally or from online, on the Web/Internet, capable of running the latest iPadOS versions.
There are PLENTY of less expensive, newer, older iPad models that can run the latest, current versions of iPadOS.
If you need OR ONLY able to purchase older, less expensive iPad models, look at older iPads from 2015 and later.
All of these older model iPads below, CAN, currently, run the latest releases of iPadOS 15 and the up and coming iPadOS 16 releasing sometime in the Fall of 2022.
2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )
2017,10.5 inch screen iPad iPad Pro models ( 1st gen Pencil support )
2017, 9.7 inch screen iPad 5th gen models ( NO Pencil support )
2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )
2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )
2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )
2019, 7.9 inch screen iPad Mini 5th gen models ( 1st gen Pencil support )
Get the largest internal data storage model you can afford as NO Apple iOS device has ANY expandable storage.
I am sorry that you had to learn all of this, but this does not change any of the facts regarding these very old iOS devices.
Please recycle these old devices properly and responsibly.
Sorry & Best of Luck to You!